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If you take a herbal supplement called ginkgo biloba in the hopes of keeping your mind sharp, you could be wasting your money.

According to a study published in today's issue of the Journal of the American Medical Association, the popular supplement does not prevent or delay the onset of dementia, nor is it effective against Alzheimer's disease.

In fact, taking ginkgo may even boost the risk of dementia.

Ginkgo biloba, a potent antioxidant, has long been thought to preserve memory by protecting brain cells from the harmful effects of free radicals. (Free radicals are unstable oxygen molecules that arise normally during metabolism and from pollution and cigarette smoke. If levels of free radicals become excessive - or if antioxidants are unavailable - cell damage can occur.)

Preliminary research had also suggested that ginkgo could prevent the clumping together of beta-amyloid proteins in the brain, a process linked to Alzheimer's disease.

However, more than two decades of research on ginkgo have turned up unconvincing evidence that the herb is helpful in slowing cognitive decline.

The vast majority of studies were conducted in adults who already had cognitive impairment or dementia. Studies of adults who did not have cognitive impairment yielded mixed results at best.

Today's study is the largest and longest ginkgo biloba trial performed to date.

Researchers assigned 3,069 adults aged 75 or older to take ginkgo biloba (120 milligrams twice daily) or a placebo pill for seven years to determine whether the herb could delay the onset of dementia due to any cause, including Alzheimer's disease.

Dementia refers to progressive symptoms such as memory loss, mood changes and a decline in the ability to talk, read and write caused by damage or changes to the brain. After Alzheimer's disease, the most common cause of dementia is stroke. This type is referred to as vascular dementia.

At the start of the study, participants were either not cognitively impaired or had mild cognitive impairment. (Individuals with mild impairment have memory problems not severe enough to warrant a diagnosis of Alzheimer's disease. Studies suggest that some people with mild cognitive impairment have an increased risk of progressing to Alzheimer's disease.)

After an average of 6.1 years of follow-up, ginkgo biloba had not prevented dementia and had no effect on the risk of developing Alzheimer's disease. Because the delay from initial brain changes to clinical dementia is known to be long, it's possible that ginkgo's effect - positive or negative - may take many more years to appear.

But ginkgo biloba is not without risks: The 25 per cent of participants who had cardiovascular disease prior to enrolling in the study were more likely to develop dementia if they took ginkgo biloba.

The decision on using the supplement should be discussed with your physician.

Your chances of having dementia increase as you get older, and genetics also play a role. But this certainly doesn't mean that everyone gets it. The same factors that increase your risk for heart disease - high cholesterol, high blood pressure and poorly controlled diabetes - are also linked to a greater likelihood of Alzheimer's disease and vascular dementia.

The following strategies can help keep your heart and blood vessels healthy - and may also preserve your memory as you age.

Reduce saturated

and trans fats

Research has linked higher intakes of saturated (animal) fat with a two- to threefold greater risk of Alzheimer's disease. Trans fats, found in many commercial baked goods and fried fast foods, have also been associated with an increased risk.

Choose lean cuts of meat, poultry breast and low-fat dairy products (1 per cent milk fat or less). Prepare foods with unsaturated fats such as olive oil, canola oil, flaxseed oil or non-hydrogenated margarine. Eat avocado and almonds; both are good sources of heart-healthy monounsaturated fat.

Eat more fish

Several studies have reported a lower risk of Alzheimer's disease and cognitive decline among older adults who eat fish at least twice a week. Oily fish such as salmon, trout, sardines and herring are excellent sources of DHA (docosohexanoic acid), an omega-3 fatty acid that helps keep the lining of brain cells flexible so memory messages can pass easily between cells. Omega-3 fats also have anti-inflammatory effects in the brain.

The ideal intake of DHA for brain health is not known, but experts suggest a daily intake of 500 milligrams of DHA and EPA (eicosapentanoic acid) combined for heart health - an amount that can be obtained by eating three ounces of salmon twice a week. If you don't like fish, consider taking a fish-oil capsule.

Increase vegetables

A six-year study of 3,718 people aged 65 and older reported that those who ate at least two to four servings of vegetables a day - versus less than one - had a significantly slower rate of cognitive decline.

Research suggests that leafy green vegetables such as spinach, kale, Swiss chard and rapini offer the greatest protection, probably because of their vitamin E content. (Vitamin E in foods is thought to protect brain cells from inflammation and free-radical damage.) While studies in humans have not found a link between fruit and cognitive decline, research in mice suggests blueberries can preserve memory.

Phytochemicals called

anthocyanins, plentiful in blueberries and cranberries, are thought to combat free

radicals.

Boost B-vitamin foods

An adequate intake of vitamin B12 and folate helps control blood levels of the amino acid homocysteine. Having a high homocysteine level is thought to damage artery walls and increase the risk of Alzheimer's and other forms of dementia.

To get your B vitamins, eat a varied diet. Good sources of folate include lentils, cooked spinach, asparagus, avocados and oranges. Vitamin B12 is found in lean meat, fish, poultry, dairy products, eggs and enriched soy beverages. If you're over 50, get your B12 from a multivitamin supplement, since absorption of the nutrient from foods decreases with age.

Stay active

Physical activity is associated with slower mental decline. Exercise, especially aerobic activity, increases blood flow to the brain and could help maintain the health of brain cells.

Leslie Beck, a Toronto-based dietitian at the Medcan Clinic, is on CTV's Canada AM every Wednesday. Her website is lesliebeck.com.